This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-364548, filed Dec. 22, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to a color cathode-ray tube apparatus, and more particularly to an in-line color cathode-ray tube apparatus having a structure for compensating variations in the convergence of a pair of side beams due to variations in the temperature of a deflection yoke.
An electron-gun assembly used in the in-line color cathode-ray tube apparatus emits three electron beams in line, i.e. a central beam and a pair of side beams that pass on a single plane. This type of color cathode-ray tube apparatus is designed to converge three electron beams 5R, 5G and 5B on the central point C of a phosphor screen 8 by means of an electron lens installed in the electron gun assembly 4 and a magnetic field generated by a PCM (Purity Convergence Magnet) 10 provided on the outer surface of an envelope, as is shown in FIG. 8.
Since, however, the distance from the electron gun assembly 4 to a peripheral portion P of the phosphor screen 8 is longer than the distance therefrom to the central point, the pair of side beams 5G and 5B converge in front of the phosphor screen 8 and not on it when they are directed to the peripheral portion P.
Accordingly, in the color cathode-ray tube apparatus that emits the three electron beams 5R, 5G and 5B in line, the three electron beams 5R, 5G and 5B are deflected in a horizontal direction (X direction) by a pincushion shape horizontal-deflection magnetic field 13 generated by a pair of upper and lower horizontal-deflection coils 12a and 12b that constitute a deflection yoke, as is shown in FIG. 9. In this structure, different deflection forces F are applied to the side beams 5R and 5B directed to the peripheral portion P, thereby converging the beams on the peripheral portion P as indicated by the broken lines in FIG. 8.
Concerning a display tube used increasingly for, for example, information device terminals, the horizontal-deflection frequency is being increased to satisfy a demand for higher definition.
However, the higher the horizontal-deflection frequency, the greater the heat generation of the horizontal-deflection coils, resulting in various problems due to an increase in the temperature of the deflection yoke. In particular, in the horizontal-deflection coils, the pincushion shape deflection magnetic field changes into a barrel shape due to thermal expansion of the coils. As a result, the degree of crossover of the pair of side beams increases at left and right portions of the screen, whereby misconvergence Xh occurs in which a red pattern 15R is displaced to the left from a blue pattern 15B as shown in FIG. 10, thereby degrading the quality of an image.
Japanese Patent Application KOKAI Publication No. 10-50238 discloses, as means for compensating misconvergence Xh of a pair of side beams, compensation means that comprises a diode bridge connected to horizontal-deflection coils, and a pair of correction coils connected parallel to each other and also connected to the diode bridge via a variable coil. This compensation means is, however, for compensating misconvergence due to variations in the process of manufacturing deflection coils, and hence cannot compensate for misconvergence that occurs after a color cathode-ray tube apparatus is assembled.
The present invention has been developed to solve the above-described problem and aims to provide a color cathode-ray tube apparatus capable of compensating misconvergence of a pair of side beams due to a change in the temperature of a deflection yoke incorporated therein.
To attain the aim, there is provided a color cathode-ray tube apparatus having a pair of horizontal-deflection coils for generating a horizontal-deflection magnetic field that horizontally deflects a plurality of electron beams emitted from an electron gun assembly, comprising:
compensation means for generating a magnetic field that compensates a change in the horizontal-deflection magnetic field due to a change in a temperature of the horizontal-deflection coils, the compensation means having auxiliary coils to which a current is supplied in synchronism with horizontal deflection of the electron beams, and a control element for controlling the current supplied to the auxiliary coils in accordance with a change in the temperature of the horizontal-deflection coils.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.